As discovered in obese mouse subjects, leptin is a peptide hormone composed of 167 amino acids. This hormone plays a role in regulating appetite as well as the metabolism. It functions by binding to a specific receptor of the hypothalamus. It is synthesized by white adipose tissue and is responsible for reducing the body's absorption of energy, hence its nickname "the hunger hormone". It has also be revealed that leptin levels in the blood closely correlate to the fatty mass of the individual.